1. Field of the Invention
This invention relates to a magnetic resonance imaging apparatus, which images the inside of a subject on the basis of a magnetic resonance signal radiated from the subject placed in a static magnetic field, and a radio frequency coil unit used in the magnetic resonance imaging apparatus.
2. Description of the Related Art
In magnetic resonance imaging apparatuses, QD (quadrature) has been used for a signal-receiving radio frequency coil to obtain images of a good SN ratio. For example, a QD coil formed of a circular coil and a saddle coil can obtain an SN ratio of about 1.4 times that of a circular coil alone.
On the other hand, general-purpose surface coils are used to image a region which cannot be imaged by a radio frequency coil dedicated to a specific region. A general-purpose surface coil is attached to the subject by a holding member when used.
The general-purpose surface coil is attached to the subject so as to be close to a region to be imaged as much as possible. Therefore, the general-purpose surface coil changes in attitude with respect to the static magnetic field, according to the region to be imaged.
Because of the above circumstances, a coil having a direction dependency is not used as the general-purpose surface coil. A saddle coil used for a QD coil has a direction dependency with respect to a flux direction of the static magnetic field. Therefore, a QD coil cannot be used as the general-purpose surface coil to further improve the SN ratio.
Jpn. Pat. Appln. KOKAI Pub. No. 2005-192804 discloses an RF coil, whose rotation angle in a plane parallel to the coil surface is adjustable. However, the rotation angle of the RF coil is only adjustable without changing relative positions of a plurality of unit coils.